The present invention relates generally to piezoelectric actuators and, more particularly, to a piezoelectric actuator capable of providing multiple degree of freedom positioning.
Piezoelectric actuators have long been used to adjust the position of various objects. In fact, piezoelectric actuators that position various objects have been the subject of several prior patents. For example, U.S. Pat. No. 5,043,621 to Culp, U.S. Pat. No. 4,877,957 to Okada et al., U.S. Pat. No. 4,798,989 to Miyazaki et al., and U.S. Pat. No. 4,944,580 to MacDonald et al. are all directed toward either piezoelectric actuators alone or devices employing piezoelectric actuators for the positioning thereof. A brief description of these patents will now be given.
In U.S. Pat. No. 5,043,621, Culp discloses a piezoelectric shear device comprising at least one piezoelectric shear actuator having X, Y, and Z translation shear piezoelectric portions arranged in a pyramidal stack between a support means and a positionable object. Electric potentials applied to the X, Y, and Z translation shear piezoelectric portions cause the stack to translate in three orthogonal directions. It should be noted that this patent emphasizes a pyramidal stack structure for the piezoelectric shear device.
In U.S. Pat. No. 4,877,957, Okada et al. disclose a pair of piezoelectric actuators each comprising a plurality of cube-shaped electrodes and cube-shaped piezoelectric members alternately arranged in the form of a matrix with leg portions projecting outward from the four corners and the center of the matrix. The distal ends of the leg portions projecting from the four corners of the matrix are fixed to a mounting plate, while a scanning probe holding member of a scanning type tunnel microscope is mounted on the distal end of the leg portion projecting from the center of the matrix. When electric potentials are applied to the electrodes, and hence to the piezoelectric members, the piezoelectric actuator adjusts the position of the scanning probe holding member in three orthogonal directions. It should be noted that this patent emphasizes a cube-type matrix structure for the piezoelectric actuators.
In U.S. Pat. No. 4,798,989, Miyazaki et al. disclose a piezoelectric actuator assembly comprising X-direction and Y-direction piezoelectric elements disposed, along with movable blocks, between fixed blocks located at four corners on a base. The piezoelectric actuator assembly also comprises Z-direction piezoelectric elements disposed on the movable blocks. When electric potentials are applied to the piezoelectric elements, the piezoelectric actuator assembly adjusts the position of a probe of a scanning tunneling microscope in three orthogonal directions. It should be noted that this patent emphasizes a fixed and movable block construction for the piezoelectric actuator assembly.
In U.S. Pat. No. 4,944,580, MacDonald et al. disclose a plurality of cylindrical piezoelectric drivers each comprising an annular piezoelectric tube having an inner electrode surface and at least at least three control electrodes positioned axially on the outside surface area. Each piezoelectric driver is positioned between a mirror substrate and a mounting block. Electric potentials are applied to the control electrodes so as to adjust the tilt, tip, and piston of the mirror substrate. It should be noted that this patent emphasizes an annular construction for the piezoelectric drivers.
While all of the above-described patents are directed toward either piezoelectric actuators alone or devices employing piezoelectric actuators for positioning, none are directed toward a piezoelectric actuator that is capable of providing up to six degrees of positioning freedom. Specifically, none of the above-described patents are directed toward a piezoelectric actuator that is capable of providing positioning freedom in three linear directions (x, y, z) and three rotary angles (xcfx86, xcex8, "psgr"). Such a piezoelectric actuator would understandably be desirable in those instances were both linear and rotary positioning is required. Thus, it would be both novel and desirable to provide such a piezoelectric actuator.
The present invention contemplates a piezoelectric actuator that is capable of providing up to six degrees of positioning freedom. Specifically, the piezoelectric actuator is capable of providing positioning freedom in three linear directions (x, y, z) and three rotary angles (xcfx86, xcex8, "psgr").
The piezoelectric actuator typically comprises a plurality of unit cells stacked on top of one another. Each unit cell typically comprises a base plate, a cruciform base, and a stack of piezoelectric plates. The base plate is fabricated of rigid, non-piezoelectric materials and is used to support the cruciform base. The cruciform base is fabricated of piezoelectric materials and is typically constructed by removing four square corners from a single large piezoelectric plate so as to achieve a cruciform shape which fits within the base plate. The stack of piezoelectric plates typically comprises a plurality of square piezoelectric plates bonded together and to the cruciform base.
The cruciform base and the each of the plurality of square piezoelectric plates in the stack have electrodes formed therein or deposited thereon, and motion (linear or angular) is generated by applying suitable drive voltages to the electrodes.
Accordingly, the primary objective of the present invention is to provide a piezoelectric actuator that is capable of providing up to six degrees of positioning freedom.
Other objectives and advantages of the present invention will become apparent to those skilled in the art upon reading the following detailed description and claims, in conjunction with the accompanying drawings which are appended hereto.